Native to Asia, the Hemlock Woolly Adelgid (Adelges tsugae) or HWA, is an invasive, aphid-like insect that attacks Eastern Hemlocks (Tsuga canadensis) and Carolina Hemlocks (Tsuga caroliniana). These insects are very small in size (1.5mm) and are often hard to see or find, but they can easily be identified by the white woolly masses they form on the underside of branches at the base of the Hemlock needles

Signs of Infestation

  • The appearance of cotton tuft-like masses (ovisacs) mostly on the underside of the foliage at the base of the needle. They’re about the size of the cotton on a Q-tip.
  • Premature needle drop.
  • Twig dieback.
  • Needles that change from deep green to grayish-green.
  • Thinning of the crown.

How Damage Occurs

The young Hemlock Woolly Adelgids, known as crawlers, search for suitable sites on their host tree, usually at the base of needles. They insert their long mouth parts and begin feeding on the tree’s stored starches. HWA remain in the same spot for the rest of their lives, continually feeding and developing into adults. Their feeding severely damages the canopy of the host tree by disrupting the flow of nutrients to its twigs and needles. Tree health declines and mortality usually occurs within 4-10 years.

Control is Easy

Already infected trees can be treated very easily to protect the tree from damage and to save the tree from being lost entirely. Hemlock trees can also be treated in a preventative manner in a high-risk infestation area.

Soil treatments of Imidacloprid or Dinotefuran in the springtime are effective. A trunk injection of Imidacloprid is also effective if the number of trees surpasses the label restrictions for soil treatment. Both must be applied by a licensed Pesticide Applicator.


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